Americans are probably not unique in treating philanthropy as a sort of game, with the goal of making it go down painlessly.

The ice bucket challenge sweeping the nation — or at least Facebook and Twitter — is another example. It’s a system that includes credit card companies making a Christmastime donation every time you charge a purchase, or shoe companies sending a pair to Africa when you buy one for yourself, or your pledging money for every mile that someone else runs a charity race.

On the surface there’s nothing wrong with any of this, since every dollar donated means one dollar more. But deeper down, the ice bucket challenge illustrates why it’s a problem.

The challenge benefits the ALS Association, which supports research into the degenerative condition ALS — amyotrophic lateral sclerosis, or Lou Gehrig’s disease.

As described by the association, the challenge “involves people getting doused with buckets of ice water on video, posting that video to social media, then nominating others to do the same, all in an effort to raise ALS awareness. Those who refuse to take the challenge are asked to make a donation to the ALS charity of their choice.” (The commonly suggested donation is $100.)

Plainly, there’s something of a perverse incentive here. Those pictured on Facebook or Twitter dousing themselves with ice water are ostensibly people who refused to donate.

But since dozens of celebrities have made videos of themselves getting doused — Matt Lauer, Mike Trout, Martha Stewart, etc. — we can assume that the principle has been turned around. The challenge has morphed into a device for increasing awareness and therefore fundraising for ALS research. It appears to be quite successful, since the association says it’s received $15.6 million in donations since July 29, compared with $1.8 million in the same period last year.

The first issue raised by the ice bucket challenge is whether this money is being put to its best use. That’s not a rap on the ALS Association, which gets good marks from the watchdog group Charity Navigator. Nor is it about whether ALS warrants this level of attention and charitable giving. It’s whether ALS warrants the attention, compared with other possible causes.

ALS certainly is a devastating condition for those who have it and for their families and caregivers. It’s almost invariably fatal, with most victims living two to five years after symptoms first appear, according to the Centers for Disease Control and Prevention. Researchers are still struggling to understand its causes.

But ALS is also a rare disease; the threshold specified in the federal Rare Disease Act of 2002 is a nationwide incidence of 200,000 patients. The CDC estimates the prevalence of ALS in the U.S. at about 12,000 people. The ALS Association says 30,000, but hasn’t responded to my inquiry about the discrepancy.

Even taking the ALS Association figure, the disease is rare, far outstripped by many other conditions requiring research funding. These include Alzheimer’s (an estimated 5.2 million patients in the U.S.) and diabetes (25.8 million).

Stunt philanthropy like the ice bucket challenge doesn’t accommodate these sorts of distinctions and comparisons — it just feeds whatever charity hits on a catchy device and treats all causes as essentially equivalent, distinguished only by their claim on public attention.

The result is that “the most successful charities will be those that are best at soliciting funds, not those that are best at making the world a better place,” as the British philanthropic organizer William MacAskill puts it.

Most people prompted by ice bucket publicity to make a donation probably don’t know much about ALS beyond the fact that Lou Gehrig got it (maybe they know about Stephen Hawking, too). They may assume that it’s a major public health problem, though the numbers say it’s not.

That would be all right if new donations to ALS added to the total of charitable giving. But the evidence is to the contrary. The concern of philanthropy experts like MacAskill is that high-profile fundraising campaigns end up cannibalizing other donations — those inclined to donate $100 to charity this summer, or this year, will judge that they’ve met their social obligations by spending the money on ALS.

The explosive spread of the ice bucket challenge could even end up hurting ALS fundraising in the long term. The challenge is a fad, and fads by their nature burn out — the brighter they glow, the sooner they disappear.

The hard work of philanthropy always lies in creating a sustainable donor base. But the ice bucket challenge has all the hallmarks of something that will be regarded in 2015 as last year’s thing.

Even today the connection between the ice bucket videos and ALS seems tenuous — think about how many times you heard about the ice bucket challenge or saw the hashtag #icebucketchallenge on Twitter before you had any idea that it was associated with ALS. The ALS Association may be very pleased with its haul of donated cash this summer, but here’s betting that next year’s collections will be closer to last year’s than this year’s.

You want to contribute to the fight against ALS, great. But if you’re doing it just because you saw or heard about Bill Gates, Jimmy Fallon, Justin Timberlake or Ethel Kennedy dumping ice water on their head, maybe you should give a bit more thought to where you donate your money.

Michael Hiltzik is a columnist for the Los Angeles Times. Write to him at mhiltzik@latimes.com.